Plant and method for purification of water coming from a desulphuration kerosene plant

ABSTRACT

Method for purification of process water, in particular coming from a kerosene desulphuration plant, and related plant, comprising the steps of neutralising the process water, carrying out a washing of the process water by a solvent, and biologically treating the process water with bacteria apt to degrade pollutants.

[0001] The present invention relates to a plant and to a method forpurification of process water coming from a kerosene desulphurationplant.

[0002] Several industrial plants employ among their process fluidswater, which in the plant duty cycle is subjected to pollution, thusrequiring a subsequent treatment for the purification and the disposalthereof. This problem is particularly felt in the petrochemical field,and in particular in those industrial sites comprising kerosenedesulphuration plants, e.g., of the so-called ‘Merox’ type.

[0003] Usually, petrochemical industrial sites provide a reflux disposalsection comprising a chemico-physical treatment unit and a biologicaltreatment unit in which all the process waters of the site are purified.However, waters coming from the kerosene desulphuration plant, due totheir elevated polluting power, cannot be treated in this section.Therefore, these waters have to be transferred to a remote site, whereatthey be purified and disposed of by skilled operators, usually byincineration processes. It will be understood that such a disposalentails relevant logistic complication, thus proving extremely costly aswell.

[0004] A pretreatment which sometimes is applied in the same industrialsite of the desulphuration plant for purification of waters coming fromthe latter is based on acidification and Nitrogen stripping. However,this fails to yield satisfactory results, further having the drawback ofyielding a highly polluted gaseous stream which has to be treated withactivated carbon filters, with the entailed extremely high costs.

[0005] Alternate disposal methods are based on evaporation, on oxidationwith hydrogen peroxide or other chemical substances with an equivalentoxidising power, and on oxidation by ozonisation. However, likewisemethods do not find an industrial application due to the very high costand the practical implementation and management difficulties thereof.

[0006] For example, EP-A-1 016 632 discloses a process for the treatmentof refinery soda residues, wherein a stripping step by water vapour isprovided.

[0007] The technical problem underlying the present invention is that ofproviding a method for purification and a related plant allowing toovercome the drawbacks hereto mentioned with reference to the known art.

[0008] This problem is solved with a method as set forth in claim 1.

[0009] The present invention provides several relevant advantages.

[0010] The main advantage thereof lies in that it provides an effectiveand cost-effective method for purification of water coming from akerosene desulphuration plant, implementable at the same industrial siteof the latter.

[0011] Other advantages, features, and the operation modes of thepresent invention will be made apparent in the following detaileddescription of some embodiments thereof, given by way of example andwithout limitative purposes. Reference will be made to FIG. 1 of theattached drawing, showing the flow chart of an embodiment of the plantfor purification according to the present invention.

[0012] First of all, an embodiment of the method according to theinvention for the depuration, and in particular the drainage, thedegradation and the disposal, of waters coming from a kerosenedesulphuration plant, which will hereinafter be called process water,will be described. This method will be illustrated with particularreference to waters coming from a Merox-type plant comprised in arefinery associated industrial site.

[0013] In such a plant, at the end of desulphuration the process watertypically has:

[0014] an elevated pH value, generally >10, caused by the highconcentration of free soda;

[0015] an elevated concentration of phenols, generally of a >1,000 mg/lvalue;

[0016] an elevated COD (i.e., Chemical Oxygen Demand) value,generally >20,000 mg/l; and

[0017] an elevated content of surfactants.

[0018] As it will be known to those skilled in the art, said chemicaloxygen demand indicates the amount of oxygen required to chemicallyoxidise the pollutants present in the volume unit of water, hence beingstrictly related to the organic load in the water flow under exam.

[0019] Moreover, generally such process water is also evil-smelling.

[0020] According to the invention, the method provides first of all achemico-physical treatment, aimed at eliminating the water-insolublepollutants and at carrying out a preliminary purifying action withrespect to the soluble pollutants. This chemico-physical treatment ismainly carried out through a step of neutralising the process water anda step of washing the latter with a solvent.

[0021] The invention further provides a biological treatment, in whichthe process water is degraded with the addition of biotechnologicalagents, in particular bacteria apt to degrade specific pollutants, inorder to eliminate the water-soluble pollutants.

[0022] In the present embodiment, said neutralising step provides theuse of sulphuric acid as neutralising agent, in quantities preferablyranging from 500 to 2,000 mg per litre of process water, and preferablywith a >98% concentration. The sulphuric acid is preferably metered as afunction of the current flow rate of process water and of the pH of thelatter, optionally measured downstream of the neutralising step itself.

[0023] Moreover, the neutralising step is carried out in associationwith a process water diluting step. This diluting is carried out withexternal water, preferably in a 1:1 ratio with the flow rate of theprocess water, pre-additivated with said sulphuric acid.

[0024] It will however be understood that the neutralisation of theprocess water can also be carried out according to modes alternatives tothe ones hereto described. E.g., the sulphuric acid can be inlettedafter the admixture between dilution water and process water. Moreover,an acid alternate to the sulphuric one can be employed. Furthermore, thediluting step can be totally absent, the acid being directly inlettedinto the process water. However, in this latter case a greater quantityof sulphuric acid would be required to attain the same neutralisingeffect.

[0025] Downstream of said neutralising step, the process water is thensubjected to an equalising step, during which it impounds in a tank fora predetermined period of time, preferably less than 1 hour, toregularise the water flow.

[0026] The process water is then subjected to a step of adding with asurfactant, preferably biodegradable, and it comprises, e.g., fattyalcohols in quantities preferably ranging from 500 to 2,000 mg per litreof process water. In this case as well, the quantity of surfactantinletted in the process water is preferably controlled as a function ofthe flow rate of the latter.

[0027] The presence of this latter step of the method for purificationis preferable in order to enhance the effectiveness of the subsequentsteps of the method, in particular the washing step.

[0028] The washing step provides a washing, preferably incountercurrent, of the process water with a solvent. In the presentexample, the solvent consists of meroxated kerosene, adducted with aflow rate equal to about the 10% of the flow rate of the process water.

[0029] With the washing step, a first extraction of the phenols presentin the process water, thereby decreasing the concentration thereoftowards the lawful threshold (typically 0.5 mg/l), a reduction of theCOD and a reduction of the surfactants in the water are attained.

[0030] As far as the biological treatment is concerned, in the presentexample it in turn provides a pretreating step, apt to raise the redoxpotential of the process water, and a subsequent potentiating step, aptto degrade with bacteria the pollutants of the process water. The raisein the redox potential attained in the pretreating step enhances theeffectiveness of the biological degradation carried out in thepotentiating step.

[0031] In the pretreating step the process water is additivated withbiotechnological agents of known type apt to allow, besides said raisingof the redox potential, the degradation of substances causing foulodours, thereby attaining a further abatement of the organic pollutantload. In particular, during the pretreating step in the process waterbiotechnological agents selected from a group comprising oligoelements,nutrients, enzymatic products and sporified biofixed bacteria areinletted.

[0032] After the pretreating step, the process water is subjected,according to known modes, to a controlled drainage inside the draincollector and to additivation with a deodorising agent, e.g., ofenzymatic type.

[0033] In the subsequent potentiating step, in the process waterspecific bacteria, selected from a group comprising bacteria for thedegradation of phenols, surfactants, aromatic compounds andhydrocarbons, and also biotechnological agents selected from a groupcomprising nutrients, like Nitrogen and Phosphorus, and oligoelements,are inletted.

[0034] It will be understood that the potentiating step completes theabatement of all the pollutants present in the process water. Inparticular, in this step of the method the COD value is further abatedand a final degradation of the surfactants, only partially eliminated inthe preceding chemico-physical treating step, is attained.

[0035] Preferably, during the potentiating step, in the process waterbiotechnological products containing bacterial species selected from agroup comprising: Nitrosomonas europea, Nitrosomonas subtilis, Bacillussubtilis, Bacillus licheniformis, Bacillus cereus, Pseudomonasfluorescens E, Pseudomonas putida, Pseudomonas subtilis, Alcaligenes,Lactobacillus lactiss, Lactobacillus helveticu, Trichoderma harzanium,Trichoderma reesci, and Phanerocheate chrysoporium, are inletted.

[0036] Preferably, in the biological treating step a step of increasingthe metabolic activity of the bacteria prior to the inletting thereof inthe process water, so that such activity already be at its peak uponinletting the bacteria themselves, is also provided.

[0037] The hereto mentioned biotechnological agents may be metered as afunction of the COD value of the process water.

[0038] Preferably, solely non genetically modified products are used.

[0039] An alternate embodiment also provides a further step of themethod for purification based on the use of a biofilter. This step isadvisable when the reflux treatment section cannot bear the pollutingload associated with the process water outletted from the abovedisclosed washing step.

[0040]FIG. 1 relates to a plant 1 for purification of water coming froma Merox-type kerosene desulphuration plant, comprised in arefinery-associated industrial site.

[0041] The plant 1 carries out the above described method forpurification of the process water. Therefor, this comprises two mainsequentially arranged sections, each apt to subject the process water toa different treatment, and in particular:

[0042] a first section, hereinafter referred to as chemico-physical andindicated with 2 in FIG. 1, in which the process water is mainlysubjected to neutralisation and to solvent washing; and

[0043] a section, hereinafter referred to as biological, in which theprocess water is degraded by a treatment with biotechnological agents,in particular bacteria

[0044] In the present embodiment, it is provided that the biologicalsection be implemented integrating the reflux treatment structuresusually is in the industrial site and hereto mentioned with reference tothe known art. In particular, the biological section in turn comprises apretreating unit 3 and a potentiating unit 4, the latter comprising thestructures of the biological treatment unit. These units 3 and 4respectively implement the pretreating and the potentiating steps heretodescribed with reference to the method of the invention.

[0045] Each of the hereto introduced sections of the plant forpurification 1 will hereinafter be detailed.

[0046] At the inlet to the chemico-physical section 2, the plant 1 firstof all provides means 5 for supplying the process water, adducting thelatter from a receiver usually located in the industrial site to thesection 2 itself.

[0047] Always at the inlet of the chemical-physical section 2, he plantfor purification 1 also comprises means 6 for supplying the dilutionwater.

[0048] The inlet flow rates of the process water and of the dilutionwater are controlled by respective flow control means, e.g., servovalves indicated with 51 and 61, respectively, in turn connected to acontrol unit 8 which will be described later.

[0049] Since the supplying means 5 and 6 essentially comprise tanks,conduits, pumps and valves of traditional type, hereinafter a furtherdescription thereof will be omitted.

[0050] The chemico-physical section 2 first of all provides a unit 7 foradditivation of sulphuric acid, provided via a dedicated feeder line.

[0051] In particular, the additivation unit 7 comprises adding meanslike a sulphuric acid receiver 71 and a metering pump 72 of the aciditself. The pump 72 is controlled by the above mentioned control unit 8,thereby implementing metering means apt to control the quantity ofsulphuric acid inletted in the process water as a function of the flowrate of the latter.

[0052] Furthermore, the chemico-physical section 2 comprises aneutralising unit 9, in which the dilution water additivated withsulphuric acid is admixed to the process water, in order to lower the pHvalue of the latter.

[0053] It will be now better appreciated that the employ of sulphuricacid as a neutralising agent proves extremely advantageous, since it isinexpensive and also commonly employed at a petrochemical industrialsite for other aims as well, thereby being easily adductible to theplant for purification 1.

[0054] The neutralising unit 9 provides that the dilution of the processwater be carried out directly on-line, using a first stationary mixer,it also indicated with 9, which promotes the homogenising of processwater, dilution water and sulphuric acid.

[0055] Preferably, the unit 9 is dimensioned so as to carry out thedilution in a 1:1 ratio.

[0056] Of course, variant embodiments could provide alternative dilutionmeans, e.g., a different type of mixer.

[0057] After neutralisation, the process water is sent to an apron orequalising unit 10, comprising in particular a seal-closed equalisingreservoir, it also indicated with 10.

[0058] The equalising reservoir 10 is provided with a so-calledbreathing valve 101, summarily sketched in FIG. 1. Such valve allows thedischarge of the possible developed vapours directly in an apparatus 11for the controlled drainage in a drain collector of the industrial site.In the apparatus 11, which will be detailed hereinafter, said vapoursare washed with water, and optionally with a deodoriser.

[0059] The equalising reservoir 10 further comprises a pH measurer 102,it also summarily sketched in FIG. 1, connected to said control unit 8,so as to allow a feedback control of the quantity of sulphuric acid tobe inletted in the process water at the adding unit 7.

[0060] In the present embodiment, from the equalising reservoir 10 theprocess water is piped, by a pump of traditional type, towards asurfactant adding unit 12.

[0061] The adding unit 12 comprises a second on-line stationary mixer121 and associated surfactant supplying means. The latter in turncomprises a surfactant receiver 122 and a surfactant metering pump 123of traditional type, the latter also controlled by the control unit 8 soas to implement surfactant metering means apt to control the quantity ofsurfactant inletted in the process water as a function of the flow rateof the latter.

[0062] From the second stationary mixer 121, the process water is pipedto a washing unit 13, which provides the washing thereof with meroxatedkerosene.

[0063] In the present embodiment, the washing unit 13 comprises aperforated-plate column, it also indicated with 13, for thecountercurrent washing, associated with level control means oftraditional type schematically depicted in FIG. 1. In such column 13 acontinuous phase, consisting of the meroxated kerosene, and a dispersephase, consisting of the process water to be treated, are provided.

[0064] The structure of the column 13, e.g., the number of platesthereof, could of course vary according to the flow rate of the processwater to be treated and to the pollutant concentration. Moreover, otherapparatuses for contacting the two liquids therebetween, e.g.,filled-type columns or spray columns, could be used.

[0065] The kerosene is fed to the plate column 13 with feeding meanscomprising a reservoir 131 and kerosene metering means 132. The lattercould consist, e.g., of flow control valves of traditional type,controlled by the control unit 8.

[0066] Upon passing into the extraction column 13, the kerosene isrecovered in the top section thereof and sent, via a suitable downflowline 133 associated with pressure control means of traditional type, toa desired destination, like, e.g., a crude, gas oil or gasolinereservoir. In particular, as above mentioned, the plant for purification1 of the present embodiment is incorporated in a petrochemicalindustrial site. Hence, the kerosene exiting the column 13 can be reusedin other units of the latter.

[0067] The process water exiting the washing unit 13 is instead sent tothe biological pretreating unit 3 with a pump of traditional type.

[0068] In the present embodiment, the above mentioned control unit 8 isbased on a PLC of known type. Summarising the above, in the presentembodiment the control unit 8 manages:

[0069] the flow rate of the process water and of the dilution water bythe servo valves 51 and 61;

[0070] the sulphuric acid metering, by the related metering pump 72 andthe pH measurer 102;

[0071] the surfactant metering, by the related metering pump 123; and

[0072] the flow rate of the kerosene by the related metering means 132.

[0073] Hence, the control unit 8 allows a control of the parameters ofthe plant 1 as a function of the flow rate of the process water to betreated, and a near-total automation of the chemico-physical section 2.

[0074] For performing the control of the above mentioned variouscomponents of the plant 1, the control unit 8 provides suitable datatransmission/reception connections of traditional type, represented byhatched lines in FIG. 1.

[0075] The control unit 8 can further control a plurality of flow and/orpressure control means of traditional type, distributed over the entireplant 1, some of which are schematically depicted in FIG. 1.

[0076] It will be appreciated that the automatic control thusimplemented also ensures a safe operation of the entire plant forpurification 1.

[0077] As to the biological section of the plant 1, the pretreating unit3 mainly comprises a sealed biological tank 31 and feeding means 32 ofsaid biotechnological pretreatment agents.

[0078] In the present embodiment, the biological tank 31 has a pluralityof floating supports, apt to create a contact surface between the activebiomass, i.e., said biotechnological agents, and the pollutants stillpresent in the process water. Moreover, the tank 31 has an aerationsystem which accelerates the degrading action of such biotechnologicalagents.

[0079] The metering and feeding means 32 comprises a powder meter,inletting into the tank 31 a preset quantity of biotechnological agentsat preset time intervals, e.g., once a day.

[0080] A variant embodiment could provide that also the biotechnologicalagent metering be managed by the control unit 8 of the chemico-physicalsection 2.

[0081] From the pretreating unit 3, the process water is piped to theabove mentioned apparatus 11 for the controlled drainage into the draincollector. The apparatus 11 is preferably dual water-seal to allow awashing of vapours possibly evolving from the process water and toprevent the formation of foul odours and the leaking of possiblepollutants in the atmosphere.

[0082] The apparatus 11 also provides means for inletting in the processwater flow a deodorising agent, e.g., of enzymatic type, the meteringthereof being carried out by a liquid metering system having a flow ratewhich be constant and independent from the flow rate of the processwater to be treated.

[0083] A variant embodiment provides that also the drainage apparatus11, and in particular the metering of the deodorising agent, becontrolled by the control unit 8 as a function of the actual flow rateof the process water.

[0084] Those skilled in the art will understand that the dimensioningand the conventional parameters of the apparatus 11 can be selectedaccording to the specific needs for purification and of the industrialsite.

[0085] It will also be appreciated that the action of the bacteria addedin the pretreating step continues along the petrochemical plant draincollector, providing a remarkable reduction of the organic load actuallyreaching an outside purifier.

[0086] The process water is then piped to the potentiating unit 4, whichprovides, besides the treatments usually provided in the knownpurification plants, a treatment with the biotechnological agents, andin particular specific bacteria, hereto mentioned with reference to themethod of the invention.

[0087] In the present embodiment, the additivation with the bacteria andthe other above disclosed products is automatically carried out byfeeding means 41. The latter comprises an additivation system, sometimesreferred to as ‘rouser’ by the experts, apt to increase the metabolicactivity of the bacteria prior to the inletting thereof into thebiological section of the plant for purification 1.

[0088] An alternative embodiment of the additivation system providesinstead a powder meter inletting in the plant for purification thebacterial products directly as provided by the producer.

[0089] Those skilled in the art will understand that the above indicatedfirst type of additivation system is advisable when lyophilised productsbe employed, whereas the second system is more suitable for biofixedsporified products.

[0090] In the present embodiment, the feeding means 41 also comprises aprogrammable nutrient and bacteria meter, allowing to inlet fixedquantities of bacteria and nutrients at preset time intervals.

[0091] A variant embodiment provides instead that said nutrient andbacteria meter be manually operated.

[0092] Another variant further provides that the metering of thebacteria be controlled as a function of the COD values found inlaboratory analyses. This control could be manually carried out ormanaged by a control unit, e.g., the above described control unit 8,with feedback control techniques of traditional type.

[0093] Those skilled in the art will understand that all the units ofthe above described plant for purification could be dimensioned so as tosatisfy specific needs related to the properties of the water to betreated, e.g., to emphasise the role of some units, and, therefore, ofsome steps of the treatment for purification, with respect to theothers.

[0094] Several further embodiments of the plant and the method of theinvention will hereinafter be illustrated.

[0095] An alternative embodiment of the method for purification providesthat the process waters be pretreated with biodegradable surfactantsdirectly into the stocking reservoir of the petrochemical plant oforigin, in order to recover a fraction of the hydrocarbon presenttherein and to partially reduce the initial polluting load of theprocess water.

[0096] Another embodiment provides that, immediately upstream of thewashing unit, the process water be heated at a temperature preferablycomprised in a range of about 50÷60° C. by traditional means andtechniques, e.g., inserting inside of the equalising reservoir a coilsupplied with low-pressure steam. In this case, the breathing valvelocated topwise of the equalising reservoir could directly discharge theexcess vapours into a process water receiver.

[0097] This heating allows to accelerate water-kerosene separation inthe washing step and, in some cases, to abate a greater quantity ofphenols enhancing the in-kerosene solubility thereof.

[0098] It will be now better appreciated that the hereto disclosed plantfor purification could be integrated in the same industrial site of theMerox plant, typically near to the process water receiver.

[0099] A specific application example of the method of the inventioncarried out in the above described plant for purification willhereinafter be described. Water coming from a Merox kerosenedesulphuration plant was treated having, at the beginning of thepurification treatment, the following pollution parameter values:

[0100] COD=23,000 mg/l;

[0101] Phenols=1,700 mg/l;

[0102] Surfactants=600 mg/l; e

[0103] pH=12.5.

[0104] Firstly, a neutralising step with sulphuric acid was carried out.In particular, about 1,000 mg of concentrated (98%) sulphuric acid perlitre of process water were added to outside water in a 1:1 dilutionratio with the flow rate of the process water. The outside water and thesulphuric acid were then admixed to the process water in said stationarymixer.

[0105] At the end of the neutralising step, the process water exhibiteda pH value equal to 8.5.

[0106] The process water was then left to rest for about 30 minutes insaid equalising reservoir.

[0107] The process water was then additivated with about 1,000 mg offatty alcohols per litre of process water.

[0108] The process water was then piped in said plate column for thestep of washing with meroxated kerosene. At the end of this step, theprocess water exhibited: COD=11,000 mg/l; Phenols=700 mg/l; Surfactants(naphtenates)=300 mg/l; and pH=8.5.

[0109] The process water was then subjected to the biological treatment.

[0110] In particular, in the pretreating unit, the process water wasadditivated with about 0.5 kg/day of bacterial products and withnutrients and oligoelements, raising the redox potential thereof fromabout −300 mV to positive values.

[0111] In the potentiating unit, in the process water the followingbacterial species were inletted: Nitrosomonas europea, Nitrosomonassubtilis, Bacillus subtilis, Bacillus licheniformis, Bacillus cereus,Pseudomonas fluorescens E, Pseudomonas putida, Pseudomonas subtilis,Alcaligenes, Lactobacillus lactiss, Lactobacillus helveticu, Trichodermaharzanium, Trichoderma reesci, e Phanerocheate chrysoporium.

[0112] Thus, for the process water, pollution parameter valuescompatible with the lawful limits regulating water discharge, inparticular: COD<160 mg/l; Phenols<0.5 mg/l; Surfactants<2 mg/l; andpH=5.5÷9.5, were attained.

[0113] It will be understood that the plant and the associated methodfor purification of the invention could also be applied to kerosenedesulphuration plants other than the Merox one hereto considered.Moreover, the invention could effectively be applied in all thoseindustrial sites, especially the petrochemical ones, having plantsyielding relatively reduced flows of highly polluted water. In thesecases, the type of solvent for carrying out said washing step could varyto conform to the specific needs of the industrial site in which theplant for purification of the invention is applied.

[0114] The present invention has hereto been described with reference topreferred embodiments thereof. It is understood that there could beother embodiments afferent to the same inventive concept, all fallingwithin the protective scope of the appended claims.

1. A method for purification of process water coming from a kerosenedesulphuration plant, comprising the steps of: neutralising the processwater; carrying out a washing of the process water by a solvent; andbiologically treating the process water with bacteria apt to degradepollutants, wherein said washing step provides a countercurrent washingof the process water using meroxated kerosene as a solvent. 2-24.(canceled)
 25. The method according to claim 1, wherein saidneutralising step provides the use of sulphuric acid as a neutralisingagent.
 26. The method according to claim 25, wherein said neutralisingstep is carried out using concentrated (>98%) sulphuric acid in aquantity comprised in a range of about 500 to 2,000 mg per litre ofprocess water.
 27. The method according to claim 1, wherein saidneutralising step provides that the quantity of neutralising agentinletted in the process water be controlled as a function of the flowrate of the latter.
 28. The method according to claim 27, wherein thequantity of neutralising agent inletted in the process water iscontrolled as a function of the pH of the latter, measured downstream ofsaid neutralising step.
 29. The method according to claim 1, whereinsaid neutralising step provides a dilution of the process water.
 30. Themethod according to claim 29, wherein said dilution is carried out in a1:1 ratio.
 31. The method according to claim 1, comprising a step ofequalising the process water downstream of said neutralising step. 32.The method according to claim 1, comprising, upstream of said washingstep, a step of adding a surfactant.
 33. The method according to claim32, wherein the quantity of surfactant inletted in the process water isregulated as a function of the flow rate of the latter.
 34. The methodaccording to claim 32, wherein said surfactant comprises fatty alcohols.35. The method according to claim 34, wherein said step of adding asurfactant is carried out using fatty alcohols in a quantity comprisedin a range of about 500 to 2,000 mg per litre of process water.
 36. Themethod according to claim 1, wherein said meroxated kerosene has a flowrate equal to about 10% of the flow rate of process water.
 37. Themethod according to claim 1, wherein said biological treating stepprovides that said bacteria be selected from a group comprising bacteriafor the degradation of phenols, surfactants, aromatic compounds andhydrocarbons.
 38. The method according to claim 1, wherein saidbiological treating step provides that said bacteria be selected from agroup comprising Nitrosomonas europea, Nitrosomonas subtilis, Bacillussubtilis, Bacillus licheniformis, Bacillus cereus, Pseudomonasfluorescens E, Pseudomonas putida, Pseudomonas subtilis, Alcaligenes,Lactobacillus lactiss, Lactobacillus helveticu, Trichoderma harzanium,Trichoderma reesci and Phanerocheate chrysoporium.
 39. The methodaccording to claim 1, wherein said biological treating step provides anaddition to the process water of biotechnological agents selected from agroup comprising nutrients and oligoelements.
 40. The method accordingto claim 1, wherein said biological treating step provides an additionto the process water of biotechnological agents metered as a function ofthe COD value of the process water.
 41. The method according to claim 1,wherein said biological treating step comprises a pretreating step, aptto raise the redox potential of the process water, and a subsequentdegrading step, apt to degrade the pollutants in the process water bybacteria.
 42. The method according to claim 41, wherein said pretreatingstep provides the inletting in the process water of biotechnologicalagents selected from a group comprising oligoelements, enzymaticproducts and bacteria.
 43. The method according to claim 42, whereinsaid bacteria are biofixed sporified.
 44. The method according to claim1, comprising a step of adding a deodorising agent to the process water.45. The method according to claim 1, comprising a step of treating by abiofilter.
 46. The method according to claim 1, comprising, upstream ofsaid washing step, a step of heating the process water.
 47. The methodaccording to claim 46, wherein said heating step provides a heating ofthe process water at a temperature comprised in a range of about 50 to60° C.